1. Field Of The Invention
This invention relates generally to suspension systems and methods for isolating and reducing the transmission of vibratory motion between an object and a base and, more particularly, to a compact omnidirectional vibration isolation or suspension system that exhibits low stiffness, high damping to limit resonant responses of the system, effective isolation at the higher frequencies, high isolator resonant frequencies, and can accommodate changing weight loads without significantly degrading isolation system performance.
2. Description of the Related Art
The problems caused by unwanted vibration on motion-sensitive equipment and devices have been widely researched and numerous solutions to prevent or reduce the transmission of vibratory motion have been proposed and developed. Many of the devices designed to reduce the transmission of unwanted vibration between an object and its surroundings, commonly called vibration isolators or suspension devices, have utilized various combinations of elements such as resilient pads made from a variety of materials, various types of mechanical springs, and pneumatic devices. There are, however, shortcomings and disadvantages associated with these particular prior art isolation systems which prevent them from obtaining low system natural frequencies and from limiting resonant responses to low values while providing high isolation performance at the higher frequencies.
These shortcomings and disadvantages of prior art systems were addressed through my development of a novel vibration isolation system and novel devices and methods for retrofitting existing vibrating isolation systems described in my application Ser. No. 07/395,093, filed Aug. 16, 1989, entitled Vibration Isolation System, my application filed Apr. 8, 1991, entitled "DAMPED VIBRATION ISOLATION SYSTEM," and my co-pending application, Ser. No. 708,995, filed May 31, 1991, entitled "VIBRATION ISOLATION SYSTEM," which are all hereby incorporated by reference in this present application. The particular vibration isolation system described in my three applications and utilized in connection with the present invention provides versatile vibration isolation by exhibiting low stiffness in an axial direction (generally the direction of the payload weight) and any direction substantially transverse to the axial direction (generally a horizontal direction). The particular system utilizes a combination of isolators that can be connected together axially in series to provide omnidirectional isolation. Each isolator is designed to isolate either the axial or the transverse component of any vibratory motion to effectively isolate vibrations in all directions. In subsequent discussions, an axial-motion isolator will be referred to as a vertical-motion isolator, and the system of axial-motion isolators will be referred to as the vertical-motion isolation system. Similarly, a transverse-motion isolator will be referred to as a horizontal-motion isolator, and the system of transverse-motion isolators will be referred to as the horizontal-motion isolation system.
In the embodiments described in my co-pending applications, the isolator relies on a principle of loading a particular elastic structure which forms the isolator or a portion of it (the loading being applied by either the supported weight or by an external loading mechanism) to approach the elastic structure's point of elastic instability. This loading to approach this point of elastic instability, also called the "critical buckling load" of the structure, causes a substantial reduction of either the vertical or the horizontal stiffness of the isolator to create an isolation system that has low stiffness (that can be made zero or near zero) in the vertical and in any horizontal direction, and increases the damping inherent in the structure. While stiffness is reduced, these isolators still retain the ability to support the payload weight.
If the load on an elastic structure with an instability is greater than the critical buckling load, the excessive load will tend to propel the structure into its buckled shape, creating a "negative-stiffness" or "negative-spring-rate" mechanism. By combining a negative-stiffness mechanism with a spring, adjusted so that the negative stiffness cancels or nearly cancels the positive stiffness of the spring, one obtains a device that can be placed at or near its point of elastic instability. The magnitude of the load causing the negative stiffness can be adjusted, creating an isolator that can be "fine tuned" to the particular stiffness desired.